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United States Patent |
5,791,661
|
Reyes
|
August 11, 1998
|
Compliant chuck jaws
Abstract
A chuck has a plurality of top jaws for engaging a workpiece. Each top jaw
has a recess and a slot that extend completely through the top jaw. The
recess and slot allow the forward end of the top jaw to deflect in a
rearward direction. This motion allows the jaws to maintain even pressure
on the workpiece instead of cocking, thereby minimizing deflection of the
workpiece during machining. The slot defines a rearward facing shoulder on
the forward end. The maximum deflection of the forward end is limited by
the width of the slot. The distance of deflection may be limited by pins
located within holes extending through the jaw perpendicular to the slot.
Inventors:
|
Reyes; Peter A. (6700 Hadley Dr., Fort Worth, TX 76180)
|
Appl. No.:
|
735674 |
Filed:
|
October 23, 1996 |
Current U.S. Class: |
279/123; 82/1.11; 279/153; 279/154 |
Intern'l Class: |
B23B 031/16 |
Field of Search: |
279/123,152-154,110
82/1.11
|
References Cited
U.S. Patent Documents
2859044 | Nov., 1958 | Buck et al.
| |
2903268 | Sep., 1959 | Buck et al.
| |
3160042 | Dec., 1964 | Grand | 279/154.
|
4046390 | Sep., 1977 | Dunham | 279/153.
|
4221391 | Sep., 1980 | Dutton.
| |
4353561 | Oct., 1982 | Peterson.
| |
5071145 | Dec., 1991 | Brook.
| |
5236207 | Aug., 1993 | Ramunas et al.
| |
Foreign Patent Documents |
1354695 | May., 1974 | GB | 279/154.
|
Primary Examiner: Bishop; Steven C.
Attorney, Agent or Firm: Bradley; James E.
Claims
I claim:
1. A top jaw with a bottom side for engaging a master jaw of a lathe chuck
having a rotational axis, the top jaw having a longitudinal axis that is
adapted to be perpendicular to the rotational axis, a forward end that is
adapted to engage a workpiece, and a rearward end, the top jaw comprising
in combination:
a recess extending through the top jaw transverse to the longitudinal axis;
and
a slot extending through the top jaw transverse to the longitudinal axis,
the slot connecting the recess to the bottom side of the top jaw, and the
slot and recess allowing the forward end of the top jaw to deflect when
the top jaw applies pressure to the workpiece, in order to maintain a
desired interface between the forward end and the workpiece.
2. The top jaw according to claim 1, wherein the slot has a width which is
reduced when the forward end deflects.
3. The top jaw according to claim 2, further comprising means for limiting
the decrease in the width of the slot when the top jaw applies pressure to
a workpiece.
4. The top jaw according to claim 1 wherein the slot has a width that is
less than the longitudinal length of the recess.
5. The top jaw according to claim 1, wherein the slot has a forward
backstop and wherein the top jaw further comprises:
a hole with a length that is parallel to the longitudinal axis and the
bottom side, the hole extending from the rearward end of the top jaw into
the slot;
a pin located in the hole, the pin having a forward end; and
means for adjusting a distance between the forward end of the pin and the
forward backstop of the slot to cause the forward backstop of the slot to
contact the forward end of the pin while at a desired maximum deflection.
6. The top jaw according to claim 1, wherein the slot has a forward
backstop and wherein the top jaw further comprises:
a threaded hole with a length that is parallel to the longitudinal axis and
the bottom side, the hole extending from the rearward end of the top jaw
into the slot;
a screw which threads into the threaded hole; and
a loading pin within the threaded hole, the pin being slidingly moveable
toward the forward backstop of the slot by the screw when the screw is
rotated into the hole to provide a desired gap between the pin and the
forward backstop of the slot prior to deflection of the top jaw, so that
deflection of the forward end of the top jaw can be limited to a point
where the pin contacts the forward backstop.
7. The top jaw according to claim 1 wherein the slot is perpendicular to
the longitudinal axis and the bottom side of the top jaw.
8. The top jaw according to claim 1 wherein the slot is located closer to
the forward end of the top jaw than to the rearward end of the top jaw.
9. In a lathe chuck having a rotational axis, a plurality of master jaws
which are radially adjustable across a face of the chuck to hold a
workpiece, a plurality of top jaws, each top jaw having a bottom side
which mates with a master jaw, and each of the top jaws having a
longitudinal axis that is perpendicular to the rotational axis, a forward
end for engaging the workpiece, a rearward end, and a left side and a
right side, each of the top jaws comprising in combination:
a recess extending through the top jaw from the left side to the right
side, transverse to the longitudinal axis;
a slot extending through the top jaw from the left side to the right side,
transverse to the longitudinal axis and perpendicular to the bottom side,
the slot joining the recess to the bottom side, the slot having a width
substantially smaller than a longitudinal dimension of the recess, and the
slot and recess allowing the forward end of the top jaw to deflect when
the top jaw applies pressure to the workpiece, thereby decreasing the
width of the slot, in order to maintain a desired interface between the
forward end and the workpiece; and
means for limiting the decrease in the width of the slot when the top jaw
applies pressure to a workpiece.
10. The lathe chuck according to claim 9, wherein the slot has a forward
backstop and a rearward wall, and wherein the means for limiting the
decrease in the width of the slot further comprises:
a hole with a length that is parallel to the longitudinal axis and the
bottom side, the hole extending from the rearward end of the top jaw;
a pin located in the hole, the pin having a forward end; and
means for adjusting a distance between the forward end of the pin and the
forward backstop of the slot to cause the forward backstop of the slot to
contact the forward end of the pin when the top jaw is at a desired
maximum deflection.
11. The lathe chuck according to claim 9, wherein the slot has a forward
backstop and wherein the means for limiting the decrease in the width of
the slot further comprises:
a threaded hole with a length that is parallel to the longitudinal axis and
the bottom side, the hole extending from the rearward end of the top jaw
into the slot;
a screw which threads into the threaded hole; and
a loading pin within the threaded hole, the pin being slidingly moveable
toward the forward backstop of the slot by the screw when the screw is
rotated into the hole to provide a desired gap between the pin and the
forward backstop of the slot prior to deflection of the top jaw so that
deflection of the forward end of the top jaw can be limited to a point
where the pin contacts the forward backstop.
12. The lathe chuck according to claim 9 wherein the slot is perpendicular
to the longitudinal axis of the top jaw.
13. The lathe chuck according to claim 9 wherein the slot is located closer
to the forward end of the top jaw than to the rearward end of the top jaw.
14. A method for creating pads for top jaws, comprising:
(a) providing a pad blank with a rotational axis;
(b) cutting the pad blank into congruent sections by making at least three
radial cuts from an axis of rotation of the pad blank, each section having
two flat radial side walls that are adjacent to side walls of other
sections, the side walls of each section being connected by an outer wall
which is provided with a notch at a junction with one of the radial side
walls;
(c) assembling the sections with the radial side walls of each section
separated from adjacent side walls by a slit having a width;
(d) releasably fastening a key to the outer wall of each of the sections
such that each of the keys extends across one of the slits into engagement
with one of the notches to prevent the width of any of the slits from
changing;
(e) loading the assembled sections into a chuck; and
(f) after completing step (e), boring a hole into the assembled sections to
create at least three pads.
15. A method for creating pads for top jaws, comprising:
(a) providing a pad blank with a rotational axis;
(b) cutting the pad blank into congruent sections by making at least three
radial cuts from an axis of rotation of the pad blank, each section having
two flat radial side walls that are adjacent to side walls of other
sections, the side walls of each section being connected by an outer wall;
(c) assembling the sections with the radial side walls of each section
separated from adjacent side walls by a slit having a width;
(d) releasably installing a key on the outer wall of each of the sections
to prevent the width of any of the slits from changing;
(e) loading the assembled sections into a chuck; and
(f) after completing step (e), boring a hole into the assembled sections to
create at least three pads; wherein steps (c) and (d) further comprise:
providing each of the sections with a notch on each of the side walls, the
notches being located near the outer wall of each of the sections and
dimensioned for closely receiving Part of one of the keys;
providing a threaded hole at each of the outer walls, each of the holes
extending radially inward through one of the notches;
each of the keys having a radial ax is and a hole that is parallel to the
radial axis;
placing each of the keys in one of the notches and orienting each of the
keys so that the hole in the key aligns with the hole in the section;
inserting a screw through each of the holes in each of the keys and
rotating the screw into the threaded hole in each of the sections in order
to rigidly secure each of the keys to its accompanying section; and
joining the sections together by placing a protruding portion of each of
the keys into the remaining notch on the mating adjacent section.
16. A method for truing a forward face on each of a plurality of top jaws
of a lathe chuck with a rotational axis and a cutting tool, comprising:
forming a recess across each of the faces between an upper side and a lower
side of each of the top jaws;
mounting the top jaws to the chuck;
clamping a truing ring in the recesses in the top jaws, such that the ring
is concentrically located on the axis;
rotating the chuck and moving a cutting tool into contact with the faces on
an outer side of the ring; then
moving the cutting tool into contact with the faces on an inner side of the
ring.
17. A top jaw with a bottom side for engaging a master jaw of a lathe chuck
having a rotational axis, the top jaw having a longitudinal axis that is
adapted to be perpendicular to the rotational axis, a forward end that is
adapted to engage a workpiece, and a rearward end, the top jaw comprising
in combination:
a cavity extending through the top jaw transverse to the longitudinal axis
and having a portion extending to the bottom side of the top jaw, and the
cavity being dimensioned to cause the forward end of the top jaw to
deflect when the top jaw applies clamping pressure to the workpiece in
order to maintain a desired interface between the forward end and the
workpiece.
18. The top jaw according to claim 17, wherein the cavity has a bottom
longitudinal dimension where it joins the bottom side which is reduced
when the forward end deflects.
19. The top jaw according to claim 18, further comprising an adjustable
stop which extends across the cavity parallel to the longitudinal axis
adjacent the bottom side for limiting the decrease in the bottom
longitudinal dimension of the slot when the top jaw applies pressure to
the workpiece.
Description
TECHNICAL FIELD
The present invention relates generally to lathe chuck jaws and more
particularly to lathe chuck jaws which better accommodate long workpieces.
A lathe power chuck has a body with three 120 degree radial slots. Each
slot contains a master jaw which moves radially inward and outward in
unison with the others. A replaceable top jaw mounts to each master jaw
for moving inward to grip a workpiece. When the chuck jaws in a
conventional lathe clamp down on a workpiece, the contact surfaces of the
chuck jaws sometimes tend to cock or radially deflect away from the
workpiece on their forward ends. Chuck jaws that have become worn are
especially susceptible to this problem, particularly in environments
requiring high gripping pressures. Traditional chuck jaws usually work
well under normal operating conditions. However, under high gripping
pressure or with longer workpieces, a slight deflection of the rotating
workpiece becomes a serious problem at its forward end as the deflection
is magnified over the length of the workpiece causing the workpiece to
vibrate.
In addition, top jaws have replaceable pads mounted to them which engage
the workpiece. Although pads can be purchased, a machinist may wish to
fabricate pads from soft bar stock using a lathe. While this method is
feasible, a more convenient means is needed. Furthermore, with new top
jaws, a machinist may wish to true the contact surfaces of the jaws which
receive the pads to match the jaws to the lathe. However, a convenient
means to true the jaws is needed.
DISCLOSURE OF INVENTION
In this invention, each of the top jaws has a transverse recess and slot,
with the slot connecting the recess with the bottom side. Both the recess
and the slot extend completely through the top jaw. The recess and the
slot allow a slight flexing of the contact face of the top jaw relative to
the bottom.
Preferably, each top jaw has two threaded holes that are parallel to the
central axis of the jaw and extend from a rearward end to the slot. Each
of the holes contains a set screw and a loading pin whose combined length
is less than the length of the hole. When the screw is threaded into the
hole, the screw slidingly moves the pin toward the contact face of the top
jaw. This arrangement is used to limit the deflection of the top jaw.
In operation, the jaws are clamped against a workpiece. When the contact
faces apply clamping pressure to the workpiece, the recess and slot allow
the forward end of the top jaw to deflect to remain in flush engagement
with the workpiece. This motion allows the pads to maintain even pressure
on the workpiece instead of cocking, thereby minimizing deflection of the
workpiece during machining. The slot defines a rearward facing shoulder on
the forward end. The maximum deflection of the forward end is limited by
the loading pins as the shoulder will eventually bottom out on the loading
pins.
BRIEF DESCRIPTIONS OF DRAWINGS
FIG. 1 is an isometric view of a power chuck having chuck jaws constructed
according to the invention.
FIG. 2 is a sectional side view of one of the top jaws of the chuck of FIG.
1.
FIG. 3 is a sectional top view of the top jaw of FIG. 2, taken along the
line 3--3 of FIG. 2.
FIG. 4 is an isometric view of the top jaws of FIG. 1 holding pad blanks
prior to machining into pads.
FIG. 5 is a sectional top view of one pad blank.
FIG. 6 is a top view of the top jaws holding a truing ring as they would be
configured in a chuck for truing contact faces of top jaws prior to
mounting the contact pads.
FIG. 7 is a sectional side view of two top jaws of FIG. 6, taken along the
line 7--7 of FIG. 6, and shown during a truing operation.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIG. 1, one embodiment of a chuck jaw assembly is shown. Chuck
11 has a cylindrical body 13 and a plurality of top jaws 31 that are each
removably secured to a master jaw 21. Master jaws 21 radially slide along
a top side 17 of body 13. The words "top" and "bottom" are used only for
convenience and do not refer to actual upper and lower surfaces. Each
master jaw 21 has a row of grooves 25 on a top side which engage mating
grooves 35 on a bottom side 33 of top jaw 31. Top jaw 31 is removably
secured to master jaw 21 with bolts (not shown) that extend through
sockets 45 in top jaw 31. The bolts thread into receptacles (not shown) in
master jaw 21 that align with sockets 45.
A sectional side view of one of the top jaws 31 is shown in FIG. 2. Top jaw
31 has a longitudinal axis 32 and a bottom side 33 that is parallel to
axis 32. Top jaw 31 has a replaceable insert or pad 37 that is removably
secured to a forward end or face 38 with a clamp screw 39. In an alternate
embodiment (not shown), pad 37 may be attached to top jaw 31 with a screw
that extends through a hole parallel to the longitudinal axis 32. Pad 37
is used to provide a contact surface to hold a workpiece to be machined.
Pads 37 can be for round stock, hex stock, square stock, or can be custom
made to other configurations. Each top jaw 31 has an elliptical aperture
or recess 41 that is at an acute angle relative to axis 32. Top jaw 31 has
a slot 43 that is perpendicular to axis 32 and connects recess 41 with
bottom side 33. Slot 43 is approximately one-tenth of an inch wide in the
preferred embodiment.
Both recess 41 and slot 43 extend completely through top jaw 31, from one
side to the other. Top jaw 31 has two threaded holes 51 that are parallel
to axis 32. Holes 51 extend from a rearward end 64 of top jaw 31 toward
forward end 38. Holes 51 extend through slot 43 and a slot wall 62, but
holes 51 do not completely penetrate top jaw 31. Each hole 51 contains a
set screw 53 and a loading pin 55 whose combined length is less than the
length of hole 51. When screw 53 is threaded into hole 51, screw 53
slidingly moves pin 55 toward forward end 38 of top jaw 31. If screw 53 is
advanced to full make-up, pin 55 will contact the end or backstop 63 of
hole 51. Backstop 63 should be considered as a part of slot wall 62.
The positions of pins 55 are set to provide a desired clearance between
backstop 63 and the ends of pins 55. This determination adjusts the
effective width of slot 43 and, thus, the amount of allowed deflection.
The amount of deflection required for each job is a function of the
material of the workpiece, the chuck hydraulic pressure, and the condition
of the chuck. During set-up, pins 55 are loosened and spaced apart from
backstop 63. Next, a workpiece is "preloaded" in chuck 11 by clamping top
jaws 31 on the workpiece at the desired pressure. Once the amount of
deflection required for a certain job is determined by preloading chuck
11, pins 55 are firmly locked against backstop 63 while top jaws 31 are
clamped on the workpiece. This is done to limit deflection of forward end
38 to that point. The workpiece may then be machined. This configuration
provides a more rigid condition for heavy machining loads. Top jaw 31 may
also be effectively locked from all motion while under load by simply
locking pins 55 against backstop 63 prior to applying any load. When chuck
11 is opened to load the next workpiece, forward end 38 of top jaw 31 can
flex in a forward direction from the clamped position. The forward ends of
pins 55 will now be spaced away from backstop 63.
In operation, a plurality of top jaws 31 are clamped against a workpiece
(not shown). When pad 37 applies clamping pressure to the workpiece,
recess 41 and slot 43 allow forward end 38 of top jaw 31 to deflect
relative to bottom side 33. When deflecting, the width of slot 43
decreases until pins 55 contact backstop 63. Referring to FIG. 2, zone 30
is the area of top jaw 31 which undergoes bending to achieve the required
compliant behavior. This motion allows pad 37 to maintain even pressure on
the workpiece instead of cocking, thereby minimizing deflection of the
workpiece during machining. In this motion, zone 30 of top jaw 31 acts
like a spring or a hinge.
The maximum deflection of forward end 61 is limited by the width of slot 43
and the placement of pins 55 as pins 55 will eventually contact or bottom
out on backstop 63. Pins 55 may be positioned to provide a desired gap
between pins 55 and backstop 63. In this position, forward end 38 will be
able to deflect only until pins 55 contact backstop 63 since screws 53
will stop further rearward movement of pins 55 by acting as a hard stop.
In an alternate embodiment, holes 51 may end at slot 43 (not shown) and
not penetrate slot wall 62. In this alternate embodiment, pins 55 would
simply land on slot wall 62 which serves as the backstop to limit
deflection of forward end 38.
Pads 37 may be created with this invention for matching a particular chuck.
As shown in FIG. 4, a cylindrical pad blank 71 is loaded into chuck 11.
Pad blank 71 has been previously cut into a number of congruent sections
73 equal to the number of jaws 15 utilized by chuck 11. Also, prior to
cutting pad blank 71 into sections, an annular rib 72 is cut on the
exterior of pad blank 71 to match the contours on the face of top jaw 31.
A sectional view of a single section 73 is shown in FIG. 5. Each section
73 has semi-cylindrical notches 75 located near partially cylindrical
outer wall 77. Section 73 has a threaded hole 78 at outer wall 77 which
extends radially inward. Notches 75 function as keyed slots for closely
receiving a disk 79.
Sections 73 are joined together to form cylindrical pad blank 71 by
inserting disk 79 into notch 75, inserting a screw 81 through a hole 80 in
disk 79, and threading screw 81 into hole 78 to rigidly secure disk 79.
Referring to FIG. 5, after installing a disk 79 on each section 73,
sections 73 are assembled together by inserting a protruding end 85 of
each disk 79 into the remaining notch 87 on an adjacent section 73 until
the complete pad blank 71 is assembled. Disks 79 keep sections 73 slightly
spaced apart by slots 83 and transmit torque from one section 73 to
another. Without disks 79, slippage of sections 73 relative to each other
might occur. Pad blank 71 can then be loaded into chuck 11 to be machined
by boring the three sections 73 simultaneously. After machining is
completed, pad blank 71 can be disassembled into pads 37 by reversing the
order of assembly stated above.
Referring to FIGS. 6 and 7, in another operation, face 38 of each top jaw
31 may need to be trued. In order to true one face 38, all top jaws 31
must be trimmed. Trimming operations are performed to match faces 38 with
the particular chuck. A truing ring 91 is manufactured so that when
clamped by jaws 31 in chuck 11 with the proper pressure, a light cut is
sufficient to true faces 38.
Truing ring 91 is clamped between top jaws 31 without pads 37 installed.
Truing ring 91 locates within a recess 96 on face 38 that will not be in
contact with pad 37 when pad 37 is installed. Only the contact surfaces 95
and 97 above and below recess 96 need be trued. Referring to FIG. 7,
truing ring 91 is configured to allow a cutting tool 93 to cut on upper
portion 95 of face 38 while top jaws 31 are clamped under hydraulic
pressure simulating actual conditions of use. Cutting tool 93 may also
extend through truing ring 91 in order to cut lower portion 97 of face 38.
Once the trimming operation is complete, truing ring 91 can be removed,
and pads 37 should seat properly on faces 38.
This invention has several advantages. A slot and recess in the forward
portion of the top jaws allows the jaws to deflect slightly under load in
order to maintain even gripping pressure on the workpiece. This feature
adds precision and safety by minimizing vibration of the workpiece during
machining. The jaws contain a pin and screw mechanism that is used to
limit deflection of the top jaw to provide a more rigid condition for
heavy machining loads. The invention also comprises novel means for
creating customized jaw pads and for truing the faces of the top jaws.
While the invention has been shown in some of its forms, it should be
apparent to those skilled in the art that it is not so limited, but is
susceptible to various changes without departing from the scope of the
invention.
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